1 innocent, sincere, guileless, ingenuous, true, natural, open, unartificial, genuine, simple, direct, candid, frank, honest, straightforward, above-board, uncomplicated, undevious, undeceptive, Colloq upfront, on the level, on the up and up:
Imitation is a kind of artless flattery.
2 unpretentious, unassuming, unaffected, natural, simple, naïve, unsophisticated, plain, ordinary, humble:
The remarks were those of an artless young man who meant nothing sinister.
3 unskilled, untalented, unskilful, unpractised, inexperienced, inexpert, primitive, unproficient, incompetent, inept, clumsy, crude, awkward, bungling:
Clogs must be the most artless footwear ever made.